Explanation:
While hunting for comets in the skies above 18th century France,
astronomer Charles Messier
diligently kept a list of the things
he encountered that were definitely not comets.
This is number 27 on his
now
famous not-a-comet list.
In fact, 21st century astronomers would identify it as a
planetary
nebula, but it's not a planet either, even though it may
appear round and
planet-like in a small telescope.
Messier 27 (M27) is an excellent example of a
gaseous emission nebula created
as a sun-like star runs out
of nuclear fuel in its core.
The nebula forms as the star's outer layers are expelled into
space, with a visible glow generated by atoms excited by the dying
star's intense but invisible
ultraviolet light.
Known by the popular name of the
Dumbbell
Nebula, the beautifully
symmetric interstellar gas cloud is over 2.5 light-years across and
about 1,200 light-years away in the
constellation
Vulpecula.
This impressive colour composite highlights details within
the well-studied central region and fainter, seldom imaged
features in the nebula's outer halo.
It incorporates broad and narrowband images
recorded using
filters sensitive to emission from sulfur, hydrogen and oxygen atoms.